Structural characterization quantum mechanical calculations

Fe(CO)s were able to characterize the structure of several unsaturated intermediates.Fe(CO>5 was deposited in dilute Ar, CH4, or SF5 matrices at ca. 10 K. UV irradiation generated mainly triplet Fe(CO>4 ( Fe(CO)4). Figure 10 shows the results obtained following irradiation of Fe(CO)s in an SFe matrix. The IR spectrum of Fe(CO)4 was consistent with a C2, structure, and quantum mechanical calculations found the C21, structure to be the energetic minimum on the potential energy surface of ground state Fe(CO>4. 

It is should be noted that high reactivity precludes the X-ray structural characterization of the ir-complexcs between dihalogens and olefinic acceptors. Indeed, quantum mechanical calculation of the interaction between... 

The main advances in analysis of organolithium compounds are related to their structural characterization by instrumental methods. These rely heavily on NMR spectroscopy and, when possible, on crystallographic methods, although other spectroscopic and physicochemical techniques are occasionally employed. A modern approach to the solution of complex analytical problems involves, in addition to the evidence afforded by these experimental techniques, consideration of quantum mechanical calculations for certain structures. The results of such calculations support or deny hypothetical assumptions on structural features of a molecule or possible results of a synthetic path. The following two examples illustrate these proceedings. 

The related intramolecular monoalkene complexes of R3E + cations, the nor-bornyl cations of group 14 elements (Si —> Pb), have been synthesized with TPFPB as counteranion and characterized by NMR spectroscopy in solution supported by quantum mechanical calculations.40 Only the acetonitrile complex, 73, of the plumbanorbornyl cation 13 could be characterized by X-ray crystallography. Similar to the structure of the plumbyl cation 74, the Pb atom in the acetonitrile complex 73 adopts a trigonal-bipyramidal coordination sphere with the C = C double bond and the acetonitrile in the apical positions and the Pb atom in the center of the trigonal plane (see Fig. 11 and Table XIV, for details).40... 

In the last part of this chapter, intramolecular charge transfer (ICT) in anthryl derivatives with linked donor-acceptor parts was discussed. Ultrafast spectroscopy has been applied both for structural characterization and for real-time probing of the ICT in this case. Microscopic solvation effects on the torsional motions and the ICT in the molecules have been examined by the use of their clusters with polar solvents. One of the most important problems which awaits for further studies is an ambiguous description of the electronic character of the charge-separated states in the systems. So far, high-level quantum-mechanical calculations have not been able to deal with such large molecular systems, but reliable evaluation of electronically... 

The study of solvatochromic shifts is of great importance and has received enormous theoretical attention in recent years. Progress has been achieved in the use of the self-consistent reaction field and cavity models. These advances have also shown several limitations. It is thus of great interest to have alternative procedures to calculate solvent effects. In this respect the use of Monte Carlo/Molecular Dynamics simulations has been growing. In this paper we suggest a procedure to allow a full quantum mechanical calculation of the solute-solvent system. The basic idea is to treat the solute, the solvent and its interaction by quantum mechanics. First a Monte Carlo simulation is performed to characterize the liquid structure. These structures are then used in the quantum mechanical calculation. As a liquid has not one but a great number of structures equally possible within a... 

The QUANTUM theoretical characterization of the molecular structure of polycyclic benzenoid aromatic hydrocarbons (PAHs) and the relationships of structure to the physical and chemical properties of PAHs are problems that have been of concern to theoreticians (and experimentalists) for more than 50 years. In general, quantum chemical procedures can be used successfully to correlate kinetic and thermodynamic data for PAHs. These procedures are usually restricted to the it systems of the PAHs and normally seem to yield very good results because (1) the it system properties are described accurately by quantum mechanical calculations and (2) the energetics of a given type of reaction in a group of related PAHs is mainly... 

The cations 2a-d were characterized by multinuclear NMR spectroscopy stq>ported by quantum mechanical calculations for structures and NMR chemical shifts. In all cases, a symmetrical cation is formed upon ionization, shown by one single resonance in the Si NMR spectra (see Fig. 2 for an example). In toluene nearly the same NMR chemical shifts ( H, Si, P) are measured as in... 

Aliev et al. have applied NMR spectroscopy, molecular dynamic simulations, and quantum mechanical calculations for full structural characterization in solution of some cyclic compounds (Fig. 5). The authors have performed calculations of J(H,H) couplings for the most stable conformers of the compounds studied. The analysis of the calculated J values and the comparison with experimental ones allowed establishing the population of conformers in the solution. The calculations were performed at the B3LYP/6-311+G(2d,p) theory level. 

Ionization potentials (IPs) are molecular properties which may serve to characterize molecules, as well as to understand their electronic structure, and consequently, many of their electronic properties, including their reactivity. In most cases, photoelectron spectra (U.V. radiation) are sufficiently complex to necessitate theoretical calculations in order to assign each structure visible on the spectra. Therefore, good evaluation of ionization energies IE) is essential for the interpretation of spectra and for a reliable identification of molecules, and quantum mechanical calculations are now routinely used for such purposes. 

Finding a Xe—Xe bond was unexpected, but there was a further surprise in store. In 2007, Seppelt and coworkers reported that the green [Xe2] in SbFs solution turns blue in the presence of xenon at pressures between 30 and 40 bar, i.e. when a substantial proportion of liquid xenon is present [16]. The process is reversible when the pressure is lowered. Crystals of the blue product could not be obtained, however, and characterization of this new species was reliant upon spectroscopy and comparison with the results obtained from quantum mechanical calculations. These data indicate the formation of a linear cation 1X04] (Oooh). [Xe Xe-Xe Xe], which could be seen as a dixenon adduct of [Xc2]. The calculated structure gives a central Xe—Xe bond length of 3.190 A (even longer than in [Xe2] ) and two terminal distances of 3.529 A. 

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